| | - Accelerometers mounted on the outside of the plant structure detect all structure-borne noise bursts occurring in the area monitored.
- These structure-borne bursts may be caused by loosened or detached parts, or they may be the result of sound generated by the power plant components themselves (valves opening or closing, control rods being inserted or withdrawn, pumps running, etc.).
- The background noise consists of a combination of the constant noise level and the individual sound bursts occurring during normal plant operation. To be able to detect detached or loose parts reliably, the amplitudes of the signals (bursts) produced from the structure-borne noise pulse are monitored continuously.
- Monitoring takes place in the frequency band between 1 and 10 kHz, which means that the signals are audible, too.
- When the signal amplitudes exceed specified thresholds, recording of the structure-borne noise signals from all the sensors is initiated. A highly sophisticated alarm logic decides whether a given event can be assigned to a category with which the system is already familiar, or whether the event is of a new type, in which case a KÜS alarm is annunciated.
- As the system is adaptive, it can be tailored to meet the requirements of the power plant to be monitored.
- Statistical evaluations of the burst arrival time difference between the individual sensors make it possible to distinguish clearly between parts which are loose and those which have already become detached. Accurate calculation based on the propagation time analysis indicates the location of the event, and other signal parameters (such as amplitude and frequency) provide information on the mass of the loose or detached part.
- Detection thresholds are plant-specific and are primarily a function of the velocity, shape and mass of the loose part, the design of the attached structure, the nature and length of the sound path to the sensor, and the intensity of the normal operating noise.
- It has, for example, proven possible to detect loose parts with a mass of less than 20 grams in the primary channel head of a steam generator.
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